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Heat Units Past Cutout / Irrigation and Crop Termination Issues
Many irrigated fields this year cutout early due to extreme crop evapotranspiration (ET) demand and diminishing irrigation capacity during July. A large number of fields hit the five nodes above white flower physiological stage in late July or early August. We have been anticipating an early harvest this year based on these conditions. According to Mesonet data, since August 1, and through September 2, the Altus area has obtained about 760 heat units, Tipton had about 765, Hollis about 740, and Fort Cobb about 680. This is past the 500-600 heat units past NAWF=5 trigger for irrigation termination judgment calls. Even for fields that reached 5 NAWF by the end of the first week of August, unless an extremely large boll load is present, it is likely time to seriously consider irrigation termination. Fields which were still producing productive blooms by the middle of August (few based on my observations) may need continued irrigation support. Because of drought and associated high temperatures, fields will likely wilt fairly soon after irrigation termination. Based on the Mesonet Irrigation Planner tool, for the last several days and for a May 10 planting date at Hollis, cotton ET has averaged about 0.3 inches/day. Fort Cobb data indicate about 0.25 inches/day, whereas Tipton has averaged about 0.32. The crop coefficients change once open bolls begin to appear, and the cotton ET rates will diminish somewhat.
With the latest round of triple digit heat, many fields we observed last week are closing in on harvest aid level maturity. Typically, 850 heat units past NAWF=5 can be used as a guideline to assist with assessing field maturity. It is usually best to integrate several methods including percent open bolls (60%), sharp knife, and nodes above cracked boll (NACB) techniques. I was in one field planted in April near Carnegie which was approximately 40% open last week. April planted cotton near Hollis is also nearing harvest aid application level maturity at this time.
Yield Estimation
This is the time of year when we typically get a lot of phone calls related to cotton yield estimation. Although a very risky endeavor, estimation of cotton yields could be important this year. There is a Texas A&M AgriLife Extension Service publication which deals with this issue. This publication takes a fairly simple approach and is “user friendly.”
September 4, 2012 Volume 2 Edition 14 Volume 1 Edition 7
Cotton Comments
OSU Southwest Oklahoma Research and Extension Center
Altus, OK

Heat Units Past Cutout / Irrigation and Crop Termination Issues
Many irrigated fields this year cutout early due to extreme crop evapotranspiration (ET) demand and diminishing irrigation capacity during July. A large number of fields hit the five nodes above white flower physiological stage in late July or early August. We have been anticipating an early harvest this year based on these conditions. According to Mesonet data, since August 1, and through September 2, the Altus area has obtained about 760 heat units, Tipton had about 765, Hollis about 740, and Fort Cobb about 680. This is past the 500-600 heat units past NAWF=5 trigger for irrigation termination judgment calls. Even for fields that reached 5 NAWF by the end of the first week of August, unless an extremely large boll load is present, it is likely time to seriously consider irrigation termination. Fields which were still producing productive blooms by the middle of August (few based on my observations) may need continued irrigation support. Because of drought and associated high temperatures, fields will likely wilt fairly soon after irrigation termination. Based on the Mesonet Irrigation Planner tool, for the last several days and for a May 10 planting date at Hollis, cotton ET has averaged about 0.3 inches/day. Fort Cobb data indicate about 0.25 inches/day, whereas Tipton has averaged about 0.32. The crop coefficients change once open bolls begin to appear, and the cotton ET rates will diminish somewhat.
With the latest round of triple digit heat, many fields we observed last week are closing in on harvest aid level maturity. Typically, 850 heat units past NAWF=5 can be used as a guideline to assist with assessing field maturity. It is usually best to integrate several methods including percent open bolls (60%), sharp knife, and nodes above cracked boll (NACB) techniques. I was in one field planted in April near Carnegie which was approximately 40% open last week. April planted cotton near Hollis is also nearing harvest aid application level maturity at this time.
Yield Estimation
This is the time of year when we typically get a lot of phone calls related to cotton yield estimation. Although a very risky endeavor, estimation of cotton yields could be important this year. There is a Texas A&M AgriLife Extension Service publication which deals with this issue. This publication takes a fairly simple approach and is “user friendly.”
September 4, 2012 Volume 2 Edition 14 Volume 1 Edition 7
Cotton Comments
OSU Southwest Oklahoma Research and Extension Center
Altus, OK